Interface-Guided Formation of 2D Ultrathin MnO₂ Nanosheets with Abundant Oxygen Defects for High Performance Supercapacitors

Interface-guided formation of 2D ultrathin MnO2 nanosheets (IGMO) with abundant oxygen vacancies was performed by a facile single pot method. This method utilizes the interface between water and ethanol to grow ultrathin oxygen-defect rich nanosheets under the assistance of ultrasound. Atomic-level crystal structure observation and valence analysis show that a great number of defects and oxygen vacancies exist in IGMO. Generous defects and sufficient oxygen vacancies provide active sites for ion adsorption and improve conductivity. The IGMO electrode demonstrated very high specific capacitance (333 F g–1 at 0.5 A g–1 and 223 F g–1 at 20 A g–1), strong cycling stability (about 10,000 cycles), and an excellent rate (66.97% of the initial capacity at 20 A g–1). It is stated that in an aqueous electrolyte, an asymmetric supercapacitor (ASC) made of IGMO (as the positively charged electrode) and commercially activated carbon (as the negatively charged electrode) could offer a maximum energy density of 51.72 W h kg–1.